Moffat still hasn't finished writing the Xmas Special script, despite starting in March. (At this speed and with one or two more episodes to write plus 'Sherlock' Series 3 locked in for a January start, I'm sceptical that the original plan to shoot the Anniversary Special at the end of the Series 7 shoot is going to happen.)
I'd guess that after the Christmas special Moffat still has two episodes for season 7 to write -- 7x06 (the post-Christmas episode) and 7x13 (the season finale & lead-in to the anniversary special(s)). And then the special(s), too, before he even gets to
Sherlock (which he says he's not even thought about yet).
I saw a Moffat quote today about
Sherlock season three and why it won't film until January: "Obviously, Sherlock Holmes is off battling Captain Kirk, and Dr Watson is helping Gandalf, and I'm in the TARDIS." Only two of those are true --
Star Trek 2013 has wrapped -- and in a month only one will be true --
The Hobbit wraps in June. It's a cute quote, but it's blameshifting.
A wag on Gallifrey Base asked what would happen if the production team ran out of Moffat scripts to film. I don't think things will get quite
that bad; even pushing Moffat's scripts to the end of the line, they're still two months away from needing a Moffat script reading to go before the cameras. If Moffat gets in a hole and the BBC starts breathing down his neck, he could always bring someone in to write a script from his plot for, say, 7x06 or 7x13. Or even both. Let someone else (Chibnall) do the heavy lifting on those scripts, freeing him up to work on the more important (at least to the BBC) scripts.